Fermi acceleration along the orbit of {\eta} Carinae

The {\eta} Carinae binary system hosts the most massive stars with the highest known mass-loss rate. Its dense wind encounters the faster wind expelled by the companion, dissipating mechanical energy in the shock, accelerating particles up to relativistic energies and producing high-energy (HE) {\gamma}-rays. We used the first 7-year data of the Fermi LAT which span two passages of {\eta} Carinae at periastron. We extracted low and HE light curves and spectra in different orbital phase bins using the new PASS8 pipeline. We used particle acceleration in hydrodynamic simulations of the system in a multi-cell geometry and compared the prediction with the observations. The {\gamma}-ray emission location is compatible with {\eta} Carinae. Two emission components are distinguished. The low-energy (LE) one cuts off below 10 GeV and its flux, modulated by the orbital motion, varies by a factor < 2. Short-term variability occurs at periastron. The HE component flux varies by a factor 3-4 but differently during the two periastrons. The variabilities observed at LE and HE during the first half of the observations, match the prediction of the simulation, assuming a surface magnetic field of 500 G. The HE component and the thermal X-ray emission were weaker than expected around the second periastron suggesting a modification of the wind density in the inner wind collision region (WCR). Diffuse shock acceleration in the WCR provides a convincing match to the observations and new diagnostic tools to probe the geometry and energetics of the system. Further observations are required to explain the periastron-to-periastron HE variability and to associate it firmly with hadronic origin. {\eta} Carinae is a pevatron at periastron. Its $\nu$ flux can be detected by IceCube after many years of observations. Orbital modulations of the HE component can be distinguished from those of photo absorption by CTA.Comment: 11 pages, 8 figure

The environment of the wind-wind collision region of η\eta Carinae

$\eta$ Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and $\gamma$-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Our main goal is to use X-ray observations of $\eta$ Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within ~10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe K$\alpha$ line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.Comment: to be published in A&A, 7 pages, 9 figure

Tidal disruption of a super-Jupiter by a massive black hole

Aims: A strong, hard X-ray flare was discovered (IGR J12580+0134) by INTEGRAL in 2011, and is associated to NGC 4845, a Seyfert 2 galaxy never detected at high-energy previously. To understand what happened we observed this event in the X-ray band on several occasions. Methods: Follow-up observations with XMM-Newton, Swift, and MAXI are presented together with the INTEGRAL data. Long and short term variability are analysed and the event wide band spectral shape modelled. Results: The spectrum of the source can be described with an absorbed (N_H ~ 7x10^22 cm^{-2}) power law (\Gamma \simeq 2.2), characteristic of an accreting source, plus a soft X-ray excess, likely to be of diffuse nature. The hard X-ray flux increased to maximum in a few weeks and decreased over a year, with the evolution expected for a tidal disruption event. The fast variations observed near the flare maximum allowed us to estimate the mass of the central black hole in NGC 4845 as ~ 3x10^5 Msun. The observed flare corresponds to the disruption of about 10% of an object with a mass of 14-30 Jupiter. The hard X-ray emission should come from a corona forming around the accretion flow close to the black hole. This is the first tidal event where such a corona has been observed.Comment: 8 pages, 10 figures, 4 table

Translocation and insertion of precursor proteins into isolated outer membranes of mitochondria

Nuclear-encoded proteins destined for mitochondria must cross the outer or both outer and inner membranes to reach their final sub- mitochondrial locations. While the inner membrane can translocate preproteins by itself, it is not known whether the outer membrane also contains an endogenous protein translocation activity which can function independently of the inner membrane. To selectively study the protein transport into and across the outer membrane of Neurospora crassa mitochondria, outer membrane vesicles were isolated which were sealed, in a right-side-out orientation, and virtually free of inner membranes. The vesicles were functional in the insertion and assembly of various outer membrane proteins such as porin, MOM19, and MOM22. Like with intact mitochondria, import into isolated outer membranes was dependent on protease-sensitive surface receptors and led to correct folding and membrane integration. The vesicles were also capable of importing a peripheral component of the inner membrane, cytochrome c heme lyase (CCHL), in a receptor-dependent fashion. Thus, the protein translocation machinery of the outer mitochondrial membrane can function as an independent entity which recognizes, inserts, and translocates mitochondrial preproteins of the outer membrane and the intermembrane space. In contrast, proteins which have to be translocated into or across the inner membrane were only specifically bound to the vesicles, but not imported. This suggests that transport of such proteins involves the participation of components of the intermembrane space and/or the inner membrane, and that in these cases the outer membrane translocation machinery has to act in concert with that of the inner membrane